Land conversion to cropland is one of the major causes of severe soil erosion in Africa. This study assesses the current cropland extent and the related soil erosion risk in Rwanda, a country that experienced the most rapid population growth and cropland expansion in Africa over the last decade. The land cover land use (LCLU) map of Rwanda in 2015 was developed using Landsat-8 imagery. Based on the obtained LCLU map and the spatial datasets of precipitation, soil properties and elevation, the soil erosion rate of Rwanda was assessed at 30-m spatial resolution, using the Revised Universal Soil Loss Equation (RUSLE) model. According to the results, the mean soil erosion rate was 250 t¨ha´1¨a´1 over the entire country, with a total soil loss rate of approximately 595 million tons per year. The mean soil erosion rate over cropland, which occupied 56% of the national land area, was estimated at 421 t¨ha´1¨a´1 and was responsible for about 95% of the national soil loss. About 24% of the croplands in Rwanda had a soil erosion rate larger than 300 t¨ha´1¨a´1, indicating their unsuitability for cultivation. With a mean soil erosion rate of 1642 t¨ha´1¨a´1, these unsuitable croplands were responsible for 90% of the national soil loss. Most of the unsuitable croplands are distributed in the Congo Nile Ridge, Volcanic Range mountain areas in the west and the Buberuka highlands in the north, regions characterized by steep slopes (>30%) and strong rainfall. Soil conservation practices, such as the terracing cultivation method, are paramount to preserve the soil. According to our assessment, terracing alone could reduce the mean cropland soil erosion rate and the national soil loss by 79% and 75%, respectively. After terracing, only a small proportion of 7.6% of the current croplands would still be exposed to extreme soil erosion with a rate >300 t¨ha´1¨a´1. These irremediable cropland areas should be returned to mountain forest to foster environmental sustainability or further sustainable alternative erosion control techniques may be applied, such as applying Vetiver Eco-engineering Technology due to its economical soil erosion control and stabilization of steep slopes and the construction of erosion control dams to absorb and break down excess runoff from unusually intense storms in various parts of the watersheds.

Land use without adequate soil erosion control measures is continuously increasing the risk of soil erosion by water mainly in developing tropical countries. These countries are prone to environmental disturbance due to high population growth and high rainfall intensity. The aim of this study is to assess the state of soil erosion by water in Uganda at national and district levels, for various land cover and land use (LCLU) types, in protected areas as well to predict the impact of support practices on soil loss reduction. Predictions obtained using the Revised Universal Soil Loss Equation (RUSLE) model indicated that the mean rate of soil loss risk in Uganda's erosion-prone lands was 3.2 t·ha −1 ·y −1 , resulting in a total annual soil loss of about 62 million tons in 2014. About 39% of the country's erosion-prone lands were comprised of unsustainable mean soil loss rates >1 t·ha −1 ·y −1 . Out of 112 districts in Uganda, 66 districts were found to have unsustainable estimated soil loss rates >1 t·ha −1 ·y −1 . Six districts in Uganda were found to have mean annual soil loss rates of >10 t·ha −1 ·y −1 : Bududa (46.3 t·ha −1 ·y −1 ), Kasese (37.5 t·ha −1 ·y −1 ), Bundibugyo (28.9 t·ha −1 ·y −1 ), Bulambuli (20.9 t·ha −1 ·y −1 ), Sironko (14.6 t·ha −1 ·y −1 ) and Kotido (12.5 t·ha −1 ·y −1 ). Among the LCLU types, the highest soil loss rates of 11 t·ha −1 ·y −1 and 10.6 t·ha −1 ·y −1 were found in moderate natural forest and dense natural forest, respectively, mainly due to their locations in highland areas characterized by steep slopes ranging between 16% to 21% and their high rainfall intensity, ranging from 1255 mm·y −1 to 1292 mm·y −1 . Only five protected areas in Uganda were found to have high mean estimated mean soil loss rates >10 t·ha −1 ·y −1 : Rwenzori Mountains (142.94 t·ha −1 ·y −1 ), Mount Elgon (33.81 t·ha −1 ·y −1 ), Bokora corridor (12.13 t·ha −1 ·y −1 ), Matheniko (10.39 t·ha −1 ·y −1 ), and Nangolibwel (10.33 t·ha −1 ·y −1 ). To manage soil erosion in Uganda's protected areas, there is an urgent need to control wildfires and human-induced disturbances such as timber harvesting and soil compaction from domestic animals. Our study analysis revealed that well-established terraces and strip-cropping could significantly reduce soil loss rates in Uganda's croplands by 80% (from 1.5 t·ha −1 ·y −1 to 0.3 t·ha −1 ·y −1 ) and by 47% (from 1.5 t·ha −1 ·y −1 to 0.8 t·ha −1 ·y −1 ), respectively, well below the sustainable soil erosion tolerance rate (1 t·ha −1 ·y −1 ) for land and water conservation.